Conventionally, magneto-optical recording has been known in which an amorphous film, such as TbFeCo (terbium, iron, cobalt), a Bi (bismuth)-substitutional garnet thin film, and a metallic thin film, such as CoPt (cobalt, platinum), are used as a recording medium. These metallic thin films have vertical magnetic anisotropy and a significant polar Kerr rotation angle or Kerr ellipticity (e.g., 0.1.degree. or over) as magneto-optical effect with respect to visible light of 400-860 nm. Therefore, these metallic thin films are used as a magneto-optical recording medium.
On the other hand, an increase of recording density is always required to recording media. Although a magneto-optical recording medium is adaptable for higher-density recording compared to a conventional magnetic recording medium, still higher-density recording is desired.
An increase of recording density requires the use of light having a short wavelength. That is, short waves must be used to increase a resolution, which is determined according to the wavelength of light in use.
However, it is known that although a TbFeCo thin film, which is currently widely used as a magnetic recording medium, has a polar rotation angle of 0.3.degree. or over with respect to infrared radiation, the polar rotation angle becomes significantly smaller as the wavelength becomes shorter. Therefore, a TbFeCo thin film cannot be used for magneto-optical recording which uses short waves such ultraviolet light.
A measurement device for magneto-optical effects generally employs a xenon lamp as a light source. However, the light intensity of a xenon lamp is weak for wavelengths of 300 nm or less, and remarkably weak for wavelengths of 200 nm or less. Therefore, this device is substantially useless for measurement in an ultraviolet region. Various reports on magneto-optical effects are available, but are limited to the regions of light having longer wavelengths than that of visible light.
According to Jpn. J. Appl. Phys. Vol. 21(1993) Pt.1, No.2, pp.989-995, Proceedings of Magneto-Optical Recording International Symposium '94, J. Magn. Soc. Jpn., Vol. 19, Supplement No. S1(1995), pp, 267-270, measurement results as to magneto-optical effects of Fe- and Co-related materials are available with respect to a wavelength of about 200 nm. However, these documents merely confirm the fact that a polar rotation angle is very small for a wavelength of about 200 nm. Also, according to Physical Review B Vol. 48, No. 22, 1993 The American Physical Society, a search result as to magneto-optical effects of iron-related material is available with respect to the waves in an ultraviolet region and longer waves. However, this report is concerned only with extremely limited Fe-related material without vertical magnetic anisotropy, which is far from being usable as a magneto-optical recording medium which uses ultraviolet light.